These teachings relates to control of systems. In many systems or interest, the system output has a low pass frequency response. One example of such system is a DC to DC converter. (Other examples include, but are not limited to, servo systems, automotive/aviation controls, disk drive memories, robotics, NCC manufacturing machines.)
Switching converters, of which DC to DC converters are one variety, are used to efficiently transform to voltage and currents at on level to voltage and current of a different level. Switching converters are particularly important when either high power or battery operation require high efficiency. Switching converters are pervasive throughout many consumer products they are in almost every ball everyday items such as cell phones PDAs personal computers extra. A key feature of the DC to DC converters is its small size and low cost. This is achieved through efficient design.
DC to DC converters are used to convert an input DC voltage to an output DC voltage. Such converters may step down (buck) or step up (boost) the input DC voltage (buck-boost converters are also possible).
Conventional power supplies use Pulse Width Modulation (PWM) modulation to control the power devices used in converters. To minimize the size of the outage capacitors and improve the rejection of the output voltage to load current steps, it is desirable to have the feedback bandwidth in a DC-to-DC converter be as large as possible. This is typically achieved by designing a linear compensated control loop with a large bandwidth. Unfortunately, one of the limitations that occur is that with a normal pulse width modulated or PWM control system is that the duty cycle cannot be less than 0% and not be more than 100%. As a result, the control loop operates its desired linear form for small disturbances but for large disturbances the behavior is suboptimal and in some cases can even become unstable. The result of this is a deliberate reduction in the linear compensator bandwidth to accommodate the effect of finite control effort.
In other applications, notably small servo motors, are not as concerned with power efficiency. In these applications, linear amplifiers may be used instead of PWMs. Linear power amplifiers are limited by the amplitude of their outputs. This limitation is similar to the 0% and 100% PWM duty cycle limitations.
There is a need to provide a controller that can operate well for large disturbances.